The use of currency note validators for the purpose of authenticating currency and providing goods, services or change in return, is well known. Many of these validators include a slot opening for receiving currency notes. The note moves along a note path where it is tested for authenticity. The note is either returned by the reversal of the drive moving the note along the path, or it proceeds to a storage location.
A fraudulent activity is to retrieve a note by attaching a piece of string or tape to the note and pulling the note out, once it has been validated and credit has been given. To assist in pulling the strung note out, an invalid piece of paper may be inserted, with the rejection of the paper reversing the rollers, which makes it easier to pull out the strung note. There have been a number of attempts to counteract such “stringing” activity.
One method has been described in U.S. Pat. No. 6,179,110 assigned to Japan Cash Machine Co, and comprises a rotating slotted drum. The note passes through the slot in the centre of the drum. Once the note has passed, and while it is being validated, the drum rotates. The drum winds any string attached to the note around the drum. This method catches the majority of “strung” notes, however, it renders the machine inoperable until an operator comes to unwind the string from the drum. This results in loss of income and user frustration at an inoperable machine.
U.S. Pat. No. 5,325,952 assigned to Dixle-Jarco, Inc, describes an antiretrieval device for a currency validator. The device includes a punch plate and teeth that define a shear to cut any string or tape attached to a note. If the string or tape is not cut, any attempt to remove the note pulls it across teeth which tear or shred the note. The cutting or tearing of either the string or the note may result in portions of string or note remaining in the machine and affecting its working, thereby putting it out of service.
Another device is described in U.S. Pat. No. 5,988,345 assigned to Mars Incorporated. The validator includes two prisms mounted on opposite sides of a note pathway. A light source is provided for emitting light toward the first prism. The first prism reflects the light across the note pathway toward the second prism, with the light passing from the first to the second prism in a straight line parallel to a plane of the note pathway. A photodetector receives light reflected from the second prism. A foreign object, such as a string obstructs a portion of light reflected from the first to the second prism. This method can be extremely sensitive, and indeed is often too sensitive, as it can be affected by sunlight or torch light, or can be recalibrated by use of clear plastic strips. The extreme sensitivity of this device often results in valid notes being rejected, and frustrated users reporting a defective machine.
The applicant does not concede that the prior art discussed above forms part of the common general knowledge in the art at the priority date.
It is therefore an object of the present invention to provide a foreign object detector for currency validators that at least in part addresses one or more of the above-described problems associated with prior art detectors.